Chemical control of the invasive weeds Ambrosia artemisiifolia and Acalypha virginica in maize fields

Ambrosia artemisiifolia and Acalypha virginica are exotic weeds in Europe that are becoming key weeds in summer annual crops. In this study, different chemical weed control strategies were compared in maize: pre-emergence, pre+post emergence, post-emergence, untreated check. The study was carried out in northern Italy during 2015 at two different sites, Grugliasco and Mesero. A. virginica was present only at the Mesero site. A RCBD with 21 m2 and 25 m2 plots, and with four and three replicates was used in Grugliasco and Mesero, respectively. The efficacy of each weed control strategy was assessed by measuring plant density (plants/m2) and ground cover (%). Weed assessments were carried out about one week after the treatment application. At the first assessment, in Mesero the infestations of A. virginica and A. artemisiifolia in untreated plots were 560 plant/m2 and 70 plant/m2, respectively. At the same assessment, at Grugliasco, more than 47 plants of A. artemisiifolia were recorded. At both sites, all the compared weed control strategies showed a complete control of A. artemisiifolia infestations. In Mesero site, A. virginica infestation was completely controlled by pre and pre+post emergence treatments. At the assessment carried out after the post-emergence application the average plant density of A. virginica was 73 plant/m2 in treated plots, and 362 plants/m2 in the untreated checks, with an average efficacy about 89%. The reduced efficacy of the post-emergence strategies is probably due the advanced growing stage of A.virginica plants at the time of post-emergence application.